Four people were killed, 24 others were injured after a bus slid into a drainage at the side of a highway and overturned in south China, local police said Saturday.

All of the injured were hospitalized but one of them was in critical condition, police and hospital sources said.

The accident occurred at about 6 p.m. Saturday at the highway in Huizhou City, Guangdong Province, police said, adding that they suspected the bus fell into the drainage after the driver steered the wheel to avoid colliding with another vehicle.

Police are probing the accident, especially to check if the bus was over-loaded.